The most important thing isn't even the instant cast, but the fact that you can pick-up things in flight form - this allows you to swoop down, pick-up a thing, lift up to lose any aggro you might have, repeat. MUCH faster than having to kill those mobs.

Second, if things are close enough, you can get there with the instant 60% before you would even have finished the cast time on your mount.

No you need a flight license, as per the tooltip. Also while it does work like druid flight form for picking up quest items, etc, it also breaks if you take damage-- so if a mob gets aggro on you, it will almost certainly hit you at least once.

I seriously doubt its 60%. I saw vids of the beta with dudes flying at high speed on it.

If anything I think it copies the fast mount speed you have. So probably instant 310%.

I have it and it's definitely faster than 60%. I think it's around 100%

"It's not what we don't know that gets us into trouble; it's what we know for sure that just ain't so." ~ Mark Twain"The time you enjoy wasting is not wasted time" ~ Jesus of Nazareth"把它放在我的屁股，爸爸" ~ Dalai Lama

It's actually insanely useful. I've skipped killing so many mobs because of this sucker. You can just hover above the ground and pickup items, yes. But it can do more.
For example, the quest (alliance) in Howling Fjord where you use a torch item to destroy those plague carriages that're sprading the plague in that vykrul town? Yeah, just used Zen Flight and used the torch from the air. No need to kill a single thing. And once you're done you can mount from zen flight, no need to land at a safe spot to mount up.

It's made some quests a good bit more enjoyable for me, but I suppose your mileage may vary. Keep in mind that you don't even have access to 280 until 70 and 310 until 80 so for example for Outlands the discrepency isn't so bad if used for questing.